Medium Frequency Amplifier

 Medium Frequency Amplifier 

This circuit, Figure 7, is primarily intended for use over the 1.7MHz to 30MHz range, and will be found to provide consider able gain. RF amplifiers of this kind are generally used to im prove long distance short wave reception, to increase volume, and to reduce second channel interference on the higher fre quencies. To avoid winding coils and permit easy band changing, Denco (Clacton) miniature plug in coils may be used. These are they “Blue” (Aerial) ranges, valve type. The most useful coils will be Range 3, 1.67-5.3MHz, or 580 to 194 metres; Range 4, 5-15MHz or 60 to 20 metres; and Range 5, 10.5-31.5MHz, or 28 to 9.5 metres. Exact coverage depends on the setting of the adjustable cores, and will also be modified if VC1 is of different value. The coils are inserted in a B9A type holder. If only single range is wanted, the coil can be mounted by its threaded end, and leads are then soldered directly to the pins. VR1 is an adjustable aerial input control, as overloading may easily arise with strong signals. R1 and R2 provide the voltage for gate 2, and R3 is for source bias. The drain circuit is arranged for capacitor coupling by C4 to the aerial socket of the receiver. This lead should not be unnec essarily long, as this may cause losses, as well as picking up signals which cause second channel interference. If the lead is screened, it must be no longer than necessary. A 2.6mH short wave sectionalised radio frequency choke will be satisfactory for the frequencies mentioned. Construction is best in a metal case, which can have a hinged lid if plug-in coils are to be fitted. (An alternative, for several bands, is to use switching as shown for Figure 11.) No ganging difficul ties can arise with VC1, which is adjusted for best volume. Second channel interference is caused by signals which are 2xIF frequency from the wanted signals. With a 470kHz interme diate frequency, these offending signals will be 940kHz from the wanted transmission. As a result, interference from this cause is unlikely at low frequencies, but very probable at high frequen cies. Such second channel interference is considerably reduced, or completely avoided, by using a tuned RF stage of this kind, actual results in this direction depending on the receiver IF, and frequencies tuned. A 9v supply is adequate, and current may be drawn from the receiver if convenient. Only about 2mA to 3mA or so will be wanted. The MEM618, 40602, and 40673 will be found satisfactory here

RF AMPLIFIERS AND CONVERTERS

 RF AMPLIFIERS AND CONVERTERS

144MHz Preamplifier

This preamplifier can be used with existing 2 metre equipment,

or ahead of the 144MHz converter described later. TR1 is the

40602 or 40673.

Aerial input is to a tapping on L1, and will generally be by

co-axial feeder. In some circumstances a short vertical aerial or

whip may be used and may provide sufficient signal strength. A

high aerial will naturally increase range and many different types

of aerial for 2m reception can be obtained. Alternatively, if a start

is being made on this band, a simple dipole may be constructed.

This can be self supporting, or of stout wire, and can be about

38½in in length overall, with the feeder descending from the cen

tre. Such an aerial will have little directivlty so need not be ro

tated, and can be raised on a light pole or mast.

For 144-146MHz reception, L1 is permanently tuned to about

145MHz by T1. Input is to gate 1, from a second tapping, and R3

with the by-pass capacitor C2 provide source bias. Gate 2 is op

erated at a fixed potential derived from the divider R1/R2. Output

from TR1 drain is to the tapping on L2, which is tuned by T2. For

a narrow range of frequencies such as the 2m Amateur band,

variable tuning is not justified, especially as L1 and L2 do not

tune sharply L3 couples to the existing 2m equipment - generally

a converter working into a lower frequency receiver.

L1 is wound with 18swg or similar stout wire, enamelled or

tinned copper. It has five turns and is tapped at one turn from the

upper end in Figure 4 for G1, and two turns from the grounded

end for the aerial. The winding is 5/16th in in diameter and turns

are spaced so that the coil is ½in long. L2 is wound in the same

way with five turns, but is ¾in long and has a centre tap for the

drain. L3 consists of a single turn of insulated wire, wound over

the lower end of L2.

When building VHF units of this and similar type, a layout per

mitting short radio frequency and by-pass return connections will

be required, and Figure 4B shows a layout for Figure 4. (Note

that TR1 is shown from the top.) A printed circuit can be pre

pared to take the components, or plain perforated board (0.15in

matrix) can be used, wired below. It is convenient to insert pins to

take L1 and L2. A small aluminium box will house the amplifier,

and this allows the co-axial aerial and output sockets to be

mounted as shown.

The screen to divide the box into two sections, to separate

gate 1 and drain coils, can generally be omitted as the layout

does not allow much feedback from L2 to L1. Tapping Gate 1

and drain down L1 and L2 also contributes to stability.

A 12v supply is preferred, but this can be 9v if other equip

ment provides this voltage and is also to supply the amplifier. The

amplifier can be self-contained if a battery is included in the box,

with on-off switch in series.

The bolts MC pass through the board and box, so that they

can provide a ground return, and they require spacers or lock

nuts. (Should it be felt that full details of preparing a printed cir

cuit, or wiring on perforated board, are required, reference can

be made to handbooks No. BP30 and No. BP35, Babani Press.)

Should a resonant dipper be available, or be constructed as

shown later, this will allow L1 and L2 to be set to about 145MHz.

If the coils are made exactly as described, adjustment of T1 and

T2 should give resonance in the 2m band. However, slight

changes in the length of leads, and similar points which arise in

construction, can influence the frequency. So should either trim

mer, be fully open, stretch the associated coil slightly to separate

its turns. On the other hand, if either trimmer is fully closed, com

press the coils to bring the turns nearer together. It is possible to

experiment with the taps, for best individual results, if the coils

are wound with tinned copper wire. Resonance can later be

checked when signals are being received through the amplifier.

To do this, or tune with no dipper, adjust the trimmers (and coils if

necessary as mentioned) for best volume

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AUTOMATIC GARDEN LIGHT

 AUTOMATIC GARDEN LIGHT This circuit automatically turns on and illuminates the LEDs when the solar panel does not detect any light. It switches off when the solar panel produces more than 1v and charges the battery when the panel produces more than 1.5v + 0.6v = 2.1v

PHONE TRANSMITTER - 3

PHONE TRANSMITTER - 3 see also Phone Bug (101-200 circuits)   This circuit has poor features but you can try it and see how it performs. It   uses a PNP transistor and requires a separate antenna. It also has a supply of   less than 1.9v, via the red LED. It would be better to put 2 LEDs in series to   get a higher voltage. It is activated when the phone is picked up.
 

new 200w amplifier circuit #srelectroniclover #ac250vcircuittutorial #ci...

BATTERY MONITOR MkI

  BATTERY MONITOR MkI 

 A very simple battery monitor can be made with a dual-colour LED and a few surrounding components. The LED produces orange when the red and green LEDs are illuminated. The following circuit turns on the red LED below 10.5v The orange LED illuminates between 10.5v and 11.6v. The green LED illuminates above 11.6v The following circuit monitors a single Li-ION cell. The green LED illuminates when the voltage is above 3.5v and the goes out when the voltage falls below 3.4v. The red LED then illuminates.

ব্যাটারি মনিটর MkI   

একটি খুব সহজ ব্যাটারি মনিটর তৈরি করা যেতে পারে একটি দ্বৈত রঙের LED এবং আশেপাশের কয়েকটি উপাদান দিয়ে। লাল এবং সবুজ LED আলোকিত হলে LED কমলা রঙ তৈরি করে। নিম্নলিখিত সার্কিটটি 10.5v এর নিচে লাল LED চালু করে। কমলা LED 10.5v এবং 11.6v এর মধ্যে আলোকিত হয়। সবুজ LED 11.6v এর উপরে আলোকিত হয়। নিম্নলিখিত সার্কিটটি একটি একক Li-ION কোষ পর্যবেক্ষণ করে। ভোল্টেজ 3.5v এর উপরে থাকলে সবুজ LED আলোকিত হয় এবং ভোল্টেজ 3.4v এর নিচে নেমে গেলে নিভে যায়। তারপর লাল LED আলোকিত হয়।

SOLAR GARDEN LIGHT

SOLAR GARDEN LIGHT   This is the circuit in a $2.00 Solar Garden Light.   The circuit illuminates a white LED from a 1.2v rechargeable cell.

ROULETTE

 ROULETTE 

 This circuit creates a rotating LED that starts very fast when a finger touches the TOUCH WIRES. When the finger is removed, the rotation slows down and finally stops

LED DICE with Slow Down

 LED DICE with Slow Down 

 This circuit produces a random number from 1 to 6 on LEDs that are similar to the pips on the side of a dice. When the two TOUCH WIRES are touched with a finger, the LEDs flash very quickly and when the finger is removed, they gradually slow down and come to a stop. LED Dice with Slow Down kit is available from Talking Electronics.

POLICE LIGHTS

 POLICE LIGHTS

 These three circuits flash the left LEDs 3 times then the right LEDs 3 times, then repeats. The 

only difference is the choice of chips.

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NEGATIVE VOLTAGE -3/-13 output

 NEGATIVE VOLTAGE -3/-13 output   A negative supply can be produced by a "Charge  Pump" circuit created with a 555, diodes and   capacitors as shown in the following circuit. The   output will deliver about 50mA.

নেতিবাচক ভোল্টেজ -3/-13 আউটপুট নিম্নলিখিত সার্কিটে দেখানো 555, ডায়োড এবং ক্যাপাসিটার দিয়ে তৈরি একটি "চার্জ পাম্প" সার্কিট দ্বারা একটি নেতিবাচক সরবরাহ তৈরি করা যেতে পারে। আউটপুট প্রায় 50mA সরবরাহ করবে।